1. Field of the Invention
The present invention relates to apparatus, a system and a method for filtering suspended solids and insoluble matter from a liquid using a captured and controlled filter medium. In particular, the invention relates to improved apparatus and an improved method for filtering foreign matter from a liquid using a moving filtering bed of granular filter material of varying texture and extracting the filtered liquid from the most fine zone or layer of the filtration material.
2. Prior Art
The use of down-flow, varying texture, granular media filters, in which the filtration media is circulated on a continuing basis, being withdrawn from a lower portion of the filter bed, and raised to a wash chamber for cleansing the filtration medium and for returning the cleansed media to the filter bed, is well known.
The continuous circulation of filter media technique has been found preferable over static media filtration techniques, the latter requiring periodic backwash interruption in the filtration process. The U.S. Pat. No. 1,007,929, issued in 1911 to M. Deacon and W. Gore, discloses a hybrid filter system which uses both dynamic, or circulating filter media and static, or stable filter media filtration techniques. In this 1911 patent the dynamic portion of the filtration media moves downward in the filter container or vessel, past a particularly defined static portion of the filtration media. The inventors of this hybrid system state, " . . . it is a recognized advantage in filters that the medium near the outlet shall remain comparatively undisturbed." Although the apparatus of inventors appears functional, it is evident however, that over time, an undesirable saturation of the filter media, in the static portion of the filtration bed, is inevitable and will contribute to undesirable pressure loss, resulting in a reduction in the efficiency of the system.
Since the static filter media portion of the filtration bed is not circulated and cleansed by the same process used to circulate and cleanse the dynamic filter media portion of the filtration bed, it is apparent that the filter system disclosed in this 1911 patent, will require cleaning the static filter media by the traditional backwash method or by replacement of the captured media, or by some other cleaning process, any of which will require down time.
U.S. Pat. No. 4,060,484, issued to Austin et al, in 1977 and my U.S. Pat. No. 4,891,142, issued in 1990, both disclose filter systems of the dynamic, down-flow type. Each system employs a totally dynamic filter bed which, while entraining filtered particles to the wash portion of the system, progressively moves downward in the system cycle and passes directly against a filter media retaining sieve, where the filtered liquid or filtrate, is drawn off. Although eventually the entire filter bed media is cleansed of filtered particles, and the cleansed filter media is recycled to the filter bed, movement of the filter media past the filter retaining sieve, where recovery of the filtrate takes place, is largely uncontrolled. The teachings in both these patents disclose that the vast majority of the coarsest filter media or material, is found to be the most active, and consequently the dirtiest media in the filter bed. Although my patent teaches positioning the draw-off means within a layer of the most fine granular filter media of the filter bed, movement of the filter media, past the filter retaining sieve of the draw-off means, is virtually at an uncontrolled rate. It is acknowledged, by those skilled in the art that movement disturbances of the filter bed, particularly in the area adjacent to the retaining sieve, containing filtered particles, will cause filtered particles to dislodge and to be lost and may drive particles through the retaining sieve, thus reducing filtration efficiency. The degree of movement disturbances, as described above, is increased proportionally to the rate of downward flow or movement of the filter media.
It is also acknowledged, by those skilled in the art, that the downward velocity of a granular filter media bed, in a vessel of which the lower walls are inclined downwardly and inwardly is not uniform throughout the filter bed when portions of the bed are withdrawn from the center of the base of the vessel. It has been found that the greatest velocity of downward movement of the filter bed is in the area immediately above the point of filter media draw-off and that the slowest rate of descent of the filter bed, is along the inside of the vessel walls. The differential in filter media movement rates in the area directly over the point of filter draw-off and at the outer periphery of the bed, can be altered by the slope, inwardly and/or downwardly, of the conical or pyramidal bottom of the vessel. However, relying on the slope of the conical or pyramidal bottom, as taught in the prior art, is inefficient if conditions change requiring a change in the slope of the vessel. Furthermore, selection of a slope in the vessel wall sufficiently steep to insure that the outer periphery of the filter bed moves downwardly at a predetermined desired rate, may be too great a slope to insure sufficient capture and may not be in harmony with the operational flow of the filtration cycle.
Centrally located deflector cones, as suggested in the prior art, have relatively limited effect on the movement of the granular filter media of the filter bed and less effective on movement in the filter media adjacent the filter media retaining sieve of the filtrate recovery means. However, it is apparent from the present invention that the full potential of deflector cones in a multi-texture, granular filter environment have not been recognized nor utilized.
It is desirable to have control over the rate of movement of the granular filter media within the area of, or adjacent to a retaining sieve of a filtrate recovery means, without relying solely on the geometry of the vessel. It is further desirable that control of movement of the granular filter media be variable, to suit changing conditions and/or varying applications, without costly modifications to the vessel.
A problem is that gravity, acting on the filter media moving along and parallel to an inclined wall of a vessel, is not as efficient in moving the media as when acting on vertically moving filter media. This is because of friction between the interior of the vessel wall and the media moving along the wall and the influence of the friction extending into the filtration media.
These problems are addressed and overcome by the present invention.